A display device such as a liquid crystal display (LCD) device which illuminates a display panel using a backlight unit is publicly known.
As a backlight unit in such a display device, a side backlight unit (also described an edge light system) is widely used. Hereafter, the side backlight unit is written as the backlight unit.
The backlight unit includes a light source which is arranged close to an end face of a light guide plate. That is, in the backlight unit, a light of the light source enters the light guide plate from the end face thereof. The light which enters the light guide plate is emitted from one surface of the light guide plate toward the display panel.
In the backlight unit, a light emitting diode (LED) is widely used as the light source. Pluralities of LEDs as the light source are mounted on a substrate. A flexible printed circuit (FPC) substrate which is capable of a space-saving design is often used as the substrate. The FPC substrate is fixed to a chassis including a backlight unit using a double-stick tape or the like. The display panel is fixed to the chassis using the double-stick tape like a FPC substrate.
Japanese Patent Application Laid-Open No. 2007-148048 discloses an example of the display device with the above-mentioned backlight unit. FIG. 21 is a perspective view of the display device according to Japanese Patent Application Laid-Open No. 2007-148048, and FIG. 22 is an exploded perspective view thereof. FIG. 23A is a partially sectional view along a C-C line in FIG. 21.
As shown in the drawings, the LED 103 is arranged close to an end face of a light guide plate 111. The LED 103 is mounted on an FPC substrate 102 for a light source. The FPC substrate 102 for the light source is fixed to a chassis 104 using a double-stick tape 114. A polarizer 101a arranged in a display panel 101 is fixed to the FPC substrate 102 for the light source using a double-stick tape 106. Since the FPC substrate 102 for the light source is fixed to the chassis 104, the polarizer 101a is fixed to the chassis 104 via the FPC substrate 102.
In the display device, the LED as a light source for the backlight unit has to be positioned and fixed to the light guide plate 111 with high alignment accuracy, because the LED is a point light source and a plurality of LEDs are used. The plurality of LEDs means not only a plurality of discrete LEDs but also one or more LED arrays having a plurality of LEDs.
When a cold cathode fluorescent lamp (CCFL) which is a linear light source is employed as a light source, a brightness distribution in a longitudinal direction of the CCFL is substantially homogeneous. However, when the LED which is a point light source is used, lights from a plurality of LEDs enter the light guide plate.
Accordingly, for example, when one LED causes a positional displacement to the other LEDs, the positional relationship between this LED and an end face of the light guide plate is different from a positional relationship between the other LEDs and the end face thereof.
Therefore, the brightness distribution of lights entering the light guide plate becomes inhomogeneous due to displacement of the LED.
A design which used the LED positively is performed in order to thin a display device. In this case, thickness of the light guide plate has to be substantially equal to the dimension of the LED which is the dimension of the thickness direction of the light guide plate.
Accordingly, for example, homogeneity of the brightness distribution of the light which is incident into the guide plate deteriorates when the LED shifts in a thickness direction of the light guide plate.
For this reason, it is required that the LED is always arranged in the accurate position in a positional relation between the LED and the light guide plate.
However, the display device mentioned above includes a gap K1 between the display panel 101 and the double-stick tape 106. The position of the LED 103 moves, when external force is applied to the display panel 101 while such a gap K1 exists. Because of the positional displacement of the LED 103, the brightness distribution becomes inhomogeneous.
FIG. 23B is a diagram illustrating such disadvantage. A polarizer 101a stuck on a glass substrate 101b is fixed to an optical sheet including lens sheets 108a and 108b and a diffusion sheet 109a by the double-stick tape 106.
Then, if the external force is applied to the display panel 101, the double-stick tape 106 sticks to a protruding part 101e of the display panel 101.
Therefore, the LED 103 departs from the end face 111a of the light guide plate 111, and the brightness distribution of the light which enters the light guide plate 111 becomes inhomogeneous. Once the double-stick tape 106 sticks to the protruding part 101e, even after the external force is removed, the FPC substrate 102 for the light source does not return to the original position. Thus, the LED 103 still remains in a position which deviates from the optimal position with respect to the end face 111a of the light guide plate 111.
The reason why the double-stick tape 106 sticks to the protruding part 101e of the display panel 101 is described below.
That is, in a configuration shown in FIG. 23A, when the external force is applied toward a chassis 104 from the protruding part 101e of the display panel 101, the protruding part 101e bends toward the chassis 104.
On the other hand, when the external force is applied toward the protruding part 101e from the chassis 104, the chassis 104 is pushed up toward the protruding part 101e. 
As in any case gap K1 contracts and it is shown in FIG. 23B, the double-stick tape 106 sticks to the protruding part 101e of display panel 101. Even after the external force is removed, the double-stick tape 106 has stuck to the protruding part 101e. 
In order to solve the above-mentioned problem, Japanese Patent Application Laid-Open No. 2007-148048 discloses a display device as shown in FIGS. 24, 25A and 26.
FIG. 24 shows an exploded perspective view of the display device, and FIG. 25A shows a cross-sectional view of the display device corresponding to a portion along a C-C line in FIG. 21. FIG. 26 is a top view of the display device which has arranged a spacer to the backlight unit.
In the display device, a spacer 105 is arranged at a position which opposes the LED 103 and is located between a protruding part 101e of a glass substrate 101b and a double-stick tape 106. A double-stick tape 115 is arranged at a position which is located between a FPC substrate 102 for the light source and the double-stick tape 106, and is closer to an end part 121 of the glass substrate 101b than the spacer 105. Thereby, a gap between the protruding part 101e of the glass substrate 101b and the FPC substrate 102 for the light source is filled in.
However, in the display device mentioned above, when the FPC substrate 102 for the light source is bent so as to cover an end part 104a of the chassis 104 and an end part 102a of the FPC substrate 102 for the light source is fixed to a back face of the chassis 104, the LED 103 deviates from the optimal position with respect to the end face 111a of the light guide plate 111. Since FPC substrate 102 for the light source unsticks from chassis 104 according to the force which tries to return from the bent state to the original flat state, this positional displacement of LED 103 occurs. When the FPC substrate 102 for a light source unsticks from the chassis 104, the LED 103 deviates from the optimal position with respect to the end face 111a of the light guide plate 111.
The positional displacement of the LED 103 causes inhomogeneous brightness distribution of incident lights in the light guide plate 111 and, as a result, deteriorates display quality in the display device.
In the above description, the FPC substrate for the light source is exemplified. However, various bent FPC substrates are employed in the display device. When such FPC substrates peel from fixed positions due to a restorative force, unexpected inconvenience may arise.